Hitherto, in an information device, to select contents items (including various applications and information) to be processed, a number of operation buttons are provided. Contents items are assigned to the operation buttons. A menu is displayed on a display screen, so contents items can be selected on the screen with a jog dial, or the like while switching a display state.
When the operation buttons are correspond to contents items, the following problem takes place. In short, since the space for the operation buttons is limited in a portable device or a device installed in a limited space such as a vehicle, it cannot handle many contents items.
When a menu is displayed on a display screen by using a hierarchical menu, selection can be made from a large number of contents items. However, this requires much effort (many operations) to reach a target function or information.
There are known apparatuses solving the problems: an apparatus of setting display conditions for each piece of information and giving permission to display only information whose display conditions are satisfied by an operation of the user, thereby automatically narrowing information to be displayed (refer to, for example, Patent Document 1); and an apparatus enabling a target contents item to be specified by a small number of operations (utterance) without performing hierarchical selecting operations by using speech recognition (refer to, for example, Patent Document 2).                Patent Document 1: JP-2000-112604 A        Patent Document 2: JP-2000-20090 A        
In the apparatus disclosed in Patent Document 1, since the number of pieces of information displayed in a menu of each levels of the hierarchy is reduced, the selecting operation in each level is easy. However, a number of operations are still necessary to reach target information and the apparatus has a first problem such that the apparatus is not suitable for an environment in which the highest priority is placed on safety as in an in-vehicle device.
The user has to check the display screen many times and perform a necessary operation each time to reach target information. While the user performs the operation, attention to driving may deteriorate.
In the apparatus disclosed in Patent Document 2, since speech recognition is used, erroneous recognition of voice cannot be avoided. The apparatus has a second problem that the user has to repeat the same operation (utterance) many times in some instances.
Meanwhile, a rule-based inferring system is known as a system used for an apparatus for selecting contents items to be selected and the like is known (refer to, for example, Non-Patent Document 1).
This system expresses the knowledge of an expert in a rule form (If-Then form) and a rule is applied to a given question, thereby obtaining a solution.
An example of a rule used in an inferring system of this kind is shown as follows (1). The rule is used at the time of determining a destination adapted to a situation statement given on the basis of the destination description.IF {(season=summer) AND (weather=clear) AND (hobby=swimming)}THEN {sea}  (1)
In a condition clause of the rule, a logical determination on a situation statement of whether each of attributes to be considered (in this case, “season,” “weather,” and “hobby”) satisfies a linguistic or numerical condition (in this case, “summer,” “clear,” and “swimming”) or not is described. In the case where the condition described in the condition clause is satisfied, one determination (“sea” in this case) to be made by the system is described in a dependent clause of the rule.
As one of applications of such an inferring system, a system of executing a control (for example, “transmission of an emergency message from the system to a center,” “playing of music,” “switch-on of a TV to show news,” and “preparation of a bath”) in accordance with a result of inference obtained by the inferring system is known.
In an inferring system, in some cases, a plurality of rules which hit (satisfy the conditional clause) exist (that is, a plurality of inference results are obtained) in a given situation depending on the way of making rules. In such a case, for example, in the application apparatus, a control may be executed only on a rule which is hit for the first as a rule satisfying the conditional clause or a control may be executed on all of hit rules in order of hit.
In this case, however, there is a possibility that a rule having higher propriety is hit after a rule having low propriety. In this case, the inferring system makes a decision which is not always optimum (or which is erroneous in some cases). When it is in an optimum value search question, it corresponds to local optimization.
To solve such a problem, all of a rule group has to be constructed so that one situation description hits only one rule.                Non-Patent Document: Yoji Masubuchi, “A research and development of Mobile Workflow System for Field Service with Case and Rule Based Reasoning)” the 43rd groupware and network service workshop of Information Processing Society of Japan, GN-43-20 (2002).        
However, it has to be constructed so that logics of conditional clauses of the rules are contrary to each other (it corresponds to direct sum division of the space of situation description). It is requested to describe situations so as to be completely divided in hierarchy.
FIG. 24 shows a table of rules in a hierarchy. When it is assumed that N attributes of a situation description exist and the resolution of each attribute i (i=1 to N) is Mi, the number of situations, that is, the number of rules Ns obtained by logical combinations is expressed by Equation (2).NS=M1×M2× . . . ×MN  (2)
The more various conditional descriptions such as the environment, situation, requirement, and state of the user are reflected in a conditional clause, the number of attributes increases. The more the precision of determining each of attributes is improved, the higher the resolution Mi becomes. As a result, the number of rules described becomes enormous. There is a third problem such that the number reaches a level which cannot be realized in some cases.
In this case, there is also a fourth problem such that, as understood also from Equation (2), when an attribute of situation description is added (N is added) later, an enormous number of rules has to be also added and rules cannot be added so easily.
Further, in the case of forming all of possible combination conditions into rules and describing all of the conditions, since a number of conditions having no noticeable characteristic and unrealistic conditions are included, there is a fifth problem such that it is not efficient to describe rules by the method.
Although the number of rules can be reduced by implementing only rules which seem to be important in application, in such a case, a sixth problem occurs such that fine inference cannot be made and it is difficult to determine an important rule (attribute).